What had happened to Rachel (a small prompt to set up the story)

In this story Rachel Gardener is dead. Or is she? Traumatised from Rachel's 'death' and keeping on the down-low from the police, Zack Foster is battling with himself and he can't take it anymore. He meets y/n and things start to change for the better. But a certain string of events is sure to send things a difficult way. But what exactly?